The present invention relates to a thermal expansion valve used for refrigerating means utilized in refrigeration cycles of air conditioner, refrigeration device and the like.
In the prior art, these kinds of thermal expansion valves were used in refrigeration cycles of air conditioners in automobiles and the like. FIG. 2 shows a prior art thermal expansion valve in cross-section together with an explanatory view of the refrigerartion cycle. The thermal expansion valve 10 includes a valve body 30 formed of prismatic-shaped aluminum comprising a refrigerant duct 11 of the refrigeration cycle having a first path 32 and a second path 34, the one path placed above the other with a distance in between. The first path 32 is for a liquid-phase refrigerant passing from a refrigerant exit of a condenser 5 and through a receiver 6 to a refrigerant entrance of an evaporator. The second path 34 is for a gas-phase refrigerant passing through the refrigerant exit of the evaporator 8 towards a refrigerant entrance of a compressor 4.
An orifice 32a for the adiabatic expansion of the liquid-phase refrigerant supplied from the refrigerant exit of the receiver 6 is formed on the first path 32, and the first path 32 is connected to the entrance of the evaporator 8 through the orifice 32a and passing the path 321. The orifice 32a comprises a center line along the longitudinal direction of the valve body 30. A valve seat is formed on the entrance of the orifice 32a, and a valve means 32b supported by a valve member 32c and forming a valve structure with the valve seat exists on the valve seat. The valve means 32b and the valve member 32c are fixed together. The valve member 32c is forced by a spring means 32d, for example, a compression coil spring.
The first path 32 where the liquid-phase refrigerant from the receiver 6 is introduced is a path of the liquid refrigerant, and is equipped with an entrance port 322, and a valve chamber 35 connected thereto. The valve chamber 35 is a chamber with a floor portion, which is formed on the same axis as the center line of the orifice 32a, and is sealed by a plug 39.
Further, in order to supply driving force to the valve body 32b according to an exit temperature of the evaporator 8, the valve body 30 is equipped with a small hole 37 and a large hole 38 having a greater diameter than the hole 37 formed on the extended line of said center line axis perforating through the second path 34. A screw hole 361 for fixing a power element member 36 working as a heat sensor is formed on the upper end of the valve body 30.
The power element member 36 is comprised of a stainless steel diaphragm 36a, an upper cover 36d and a lower cover 36h each defining an upper pressure operation chamber 36b and a lower pressure operation chamber 36c formed so as to contact each other with said diaphragm in between, being divided by said diaphragm forming two sealed chambers above and under the diaphragm 36a, and a tube 36i for enclosing a predetermined refrigerant working as a diaphragm driver liquid into said upper pressure operation chamber, which is fixed to the valve body 30 through a screw 361. Said lower pressure operation chamber 36c is connected to said second path 34 through a pressure hole 36e formed concentric to the center line axis of the orifice 32a. A refrigerant vapor from the evaporator 8 is flown through the second path 34. The second path 34 is a path for the gas-phase refrigerant, and the pressure of said refrigerant vapor is loaded to said lower pressure operation chamber 36c through the pressure hole 36e.
Further, a heat sensing shaft 36f comprising a heat sensing portion 318 exposed inside the path 34 so as to cross said path 34 is formed to contact the diaphragm 36a inside the lower pressure operation chamber 36c and slidably positioned inside the large hole 38 penetrating the second path 34, which not only transmits the exit temperature of the refrigerant of the evaporator 8 to the lower pressure operation chamber 36, but also provides driving force by sliding inside said large hole 38 in response to the displacement of the diaphragm 36a accompanied by the difference in pressure inside the upper pressure operation chamber 36b and the lower pressure operation chamber 36c. An operation shaft 37f is positioned slidably inside the small hole 37 which presses the valve means 32b against the spring force of the spring means 32d in response to the displacement of the heat sensing shaft 36f. Said heat sensing shaft 36f having the diaphragm 36a contacting to its surface comprises of a stopper portion 312 having a large diameter working as a receiving portion of the diaphragm 36a, a large diameter portion 314 slidably inserted inside the lower pressure operation chamber 36c having one end surface contacting to the back surface of the stopper portion 312, and a heat sensing portion 318 having one end surface contacting to the other end surface of said large diameter portion, and the other end surface being connected to the operation shaft 37f.
The heat sensing shaft 36f is further equipped with a ring-shaped sealing member, for example, an O-ring 36g, so as to provide a sealed status between the first path 32 and the second path 34. The heat sensing shaft 36f and the operation shaft 37f are connected to each other, and the operation shaft 37f is in contact with the valve means 32b. Together, the heat sensing shaft 36f and the operation shaft 37f form a rod member which is the valve driving shaft.
In the structure of such thermal expansion valve, a known diaphragm driving liquid is filled inside the upper pressure activating chamber 36b of the upper cover 36d, and the heat of the refrigerant vapor from the refrigerant exit of the evaporator 8 flowing through the second path 34 is transmitted to the diaphragm driving liquid through the second path 34, the heat sensing portion 318 exposed to the pressure hole 36e connected to the second path 34, and the diaphragm 36a.
The diaphragm driving liquid inside the upper pressure operation chamber 36b loads pressure to the upper surface of the diaphragm 36a by turning into gas in correspondence to said heat transmitted thereto. The diaphragm 36a is displaced in the upper or lower direction according to the difference between the pressure of the diaphragm driving gas loaded to the upper surface thereto and the pressure loaded to the lower surface thereto.
The displacement of the center portion of the diaphragm 36a to the upper or lower direction is transmitted to the valve member 32b through the valve member driving shaft and moves the valve member 32b closer to or away from the valve seat of the orifice 32a. As a result, the flow rate of the refrigerant is controlled.
That is, since the temperature of the gas phase refrigerant on the exit side of the evaporator 8 is transmitted to the upper pressure operation chamber 36b, the pressure inside the upper pressure operation chamber 36b changes according to said temperature, and the exit temperature of the evaporator 8 rises. That is, when the heat load of the evaporator is increased, the pressure inside the upper pressure operation chamber 36b rises, and accordingly, the heat sensing shaft 36f or valve member driving shaft is moved to the downward direction and pushes down the valve means 32b, resulting in a wider opening of the orifice 32a. This increases the supply rate of the refrigerant to the evaporator 8, and lowers the temperature of the evaporator 8. In contrast, when the temperature of the evaporator 8 decreases and the heat load of the evaporator is lowered, the valve means 32b is driven in the opposite direction as the explanation above, resulting in a smaller opening of the orifice 32a. The supply rate of the refrigerant to the evaporator decreases, and the temperature of the evaporator 8 rises.